1. Field of the Invention
This invention relates to valves in general and in particular to control valves for use with pneumatic devices.
2. Description of the Prior Art
Many pneumatic devices require control valves that are cheap, reliable and rugged. Heretofore it has been proposed to employ a three-way ball valve of the type comprising a valve body having two axially spaced ports, a valve seat associated with each of those ports, a third port located between the other two ports, a valve member in the form of a ball which is free to move between the two valve seats and an actuating pin for urging the ball against one of the two valve seats. Such a valve is disclosed in U.S. Pat. No. 3,927,459 as the trigger-operated control valve for a pneumatic impact tool used to drive nails. However, while such a ball valve has certain advantages, it also has liabilities. For example, it suffers from the limitation that its operation is not sufficiently precise; also that the ball member may occasionally tend to impede the full flow of fluid through the side port when it is disposed intermediate of its two valve seats.
Another problem with control valves of the type shown in U.S. Pat. No. 3,927,459 is the lack of reliability in the resilient seals which serve as the valve seats. There is a tendency for the seals, which typically are washers made of an elastomer such as neoprene, butyl rubber or silicone rubber, to delaminate from its mount, i.e. to separate from the surface of the valve to which it is attached. In control valves of the type shown in U.S. Pat. No. 3,927,459, the seals 94 and 96 which are engaged by the valve member in its upper and lower positions are usually attached to their mount by a cement and/or a friction fit. As a consequence of the cycling of air that occurs when the valve is operated, however, the high pressure air will tend to intrude under the seals wherever there is a gap or weakness in the bond between the seals and their supporting surfaces and thereby cause the seals to separate from their supporting surfaces or otherwise shorten their expected life. Another problem is achieving good sealing between the ball member and the valve seats under varying ambient conditions.